Hair-care appliances in the form of curling tongs are known, for example, from DE-38 43 186 C2. Arranged within the tubular heating rod, laterally alongside the heating device, which comprises a tubular burner housing, is a rod-like thermostat which runs in the longitudinal direction of the heating device. The thermostat is designed as a control rod and, at one end, is connected mechanically to a valve device. The control rod controls the valve device in dependence on temperature, and the valve device, in turn, regulates the feed of gas to the heating device. The temperature of the curling tongs and/or the temperature of the heating rod is regulated in this way.
In the case of these curling tongs, the heating device emits its thermal energy in the form of heat radiation and free convection both to the tubular heating rod and directly to the thermostat. The influence of the heat of the heating device on the expansion of the control rod is thus considerably greater than the influence of the heat which flows from the heating rod to the control rod. On account of this arrangement, the controller obtains the largest percentage of its temperature information from the heating device, which may be configured as an open flame or as a catalyst. Accordingly, the heat acting directly on the control rod from the heating device may result in the control rod being regulated down all too prematurely, with the result that the heating rod does not heat up quickly enough. Following this regulating-down operation, the dwell time until the valve device is regulated up is then comparatively long because the cooling of the control rod, and thus the opening of the valve device, takes up a certain period of time in which rapid heating of the heating rod is diminished.
It is also found that the temperature of the heating rod during operation is not always the optimum temperature for sufficient curl shaping, i.e. the temperature of the heating rod may be too high or else also too low, because the system is self-limiting during reheating and thus only regulates the temperature of the heating rod moderately well.